1. Field of the Invention
The present invention relates to a method for forming a metal oxide film having both a surface irregularity and a predetermined pattern or either and the obtained metal oxide film by using such forming method. More particularly, the present invention relates to a method for forming a metal oxide film having a surface irregularity and the like, which is most suitable for the electrodes of electronic devices, and the obtained metal oxide film by using such forming method.
2. Description of the Related Art
Conventionally, a transparent electrode which is composed of a thin film including the metal oxide and which is formed by using a vapor deposition process on a glass substrate (hereinafter, it may be called as a metal oxide film) has been known.
However, a plastic film would be substituted for a glass substrate in view of its light weight and the necessity of a thin type electronic device.
The following formation methods have been known to form a metal film or a metal oxide film on such a plastic film.
(1) the vapor deposition method such as the vacuum deposition process or the sputtering process of metal materials or metal oxide materials.
(2) the coating method for the solution in which metal particles or metal oxide particles are dispersed into an organic binder.
However, the production cost for (1) the vapor deposition method is very high, since it is necessary to maintain the high vacuum condition, and there are problems in mass productivity and economic aspects for the vapor deposition method.
Also, (2) the coating method has the problem that the conductivity of the obtained metal film and the like is inferior to that of the metal film and the like which is obtained by the vapor deposition method.
Accordingly, the sol-gel method using metal alkoxide and its hydrolysate has been proposed as a formation method of the metal oxide film, since the obtained metal oxide film is homogeneous, transparent, and the selection range of materials for such formation method is wide.
Also, the recent study of the composite film (highbred film) which has a homogeneous property and which is composed by an inorganic polymer and an organic polymer has been carried out by further incorporating the other organic materials in order to have the new functions as well as to improve the properties.
However, since the thermal treatment process (sintering process) at a high temperature was necessary, and the continuous manufacturing method was limited, there were problems that the manufacturing cost became high and the substrate was easily heat-degraded while the heat treatment process.
Further, there was the other problem that the kind selection of the substrate was excessively limited to prevent such heat degradation of the substrate.
Therefore, instead of carrying out the thermal treatment process at a high temperature when a metal oxide film is formed by using a sol-gel method, a wavelength irradiation with ultraviolet light at 360 nm or less has been proposed for crystallizing the metal oxide film (e.g., JPH9-157855A).
Also, when a metal oxide film is formed by using a sol-gel method, a method by which a plasma treatment is carried out after forming a metal oxide gel layer on a substrate, has been proposed (e.g., JP200-327310A).
More specifically, it is the method for forming a metal oxide film by applying the predetermined plasma treatment to the metal oxide gel layer, after metal oxide sol obtained from a metal alkoxide or a metal salt as a main material on substrate, was beforehand changed into the metal oxide gel layer.
On the other hand, a transparent electrode substrate for solar batteries comprising the texturing layer having an irregularity, has been disclosed, in order to improve light conversion efficiencies and the like, in the fields such as the organic thin film solar battery (e.g., JP2008-177549A).
More specifically, it is the transparent electrode substrate for a solar battery consisting of the resin film, the texturing layer having an irregularity and the metal oxide film, wherein it is characterized in that the texturing layer having the irregularity is composed of a cured product of photo-curable composition.
Also, as an anodizing film, the method for forming a nanostructure pattern directly to a metal film or a metal oxide film has been proposed. Namely, the method for obtaining a porous material having a pore self-regularly by using an electrochemistry has been proposed (e.g., JPH2-254192A).
More specifically, as shown in FIG. 27A-FIG. 27F, it is the method for obtaining a porous material.
That is, as shown in FIG. 27A, an anodizing film (anodizing film barrier layer 202 and anodizing film porous layer 203) is formed on the surface which becomes a matrix 201 by anodizing aluminum material.
Then, as shown in FIG. 27B, the obtained anodizing film is used as the matrix 201, and a metal 205′ which is a negative mold of the porous film is filled in a pore of the matrix 201.
Further, as shown in FIG. 27C, the matrix 201 is dissolved selectively. Further, as shown in FIG. 27D, a negative mold 205 of the porous film is obtained by removing anodizing film 202, 203.
Still further, as shown in FIG. 27E, the other material 206′ is filled into the negative mold 205 of the porous film.
Lastly, as shown in FIG. 27F, a porous material 206 which has the same shape as the anodizing film is obtained by dissolving the negative mold 205 selectively.
However, according to the formation method described in JPH9-157855A, the ultraviolet irradiation exposure time is long and some substrates would easily suffer damages from the ultraviolet irradiation exposure, an ultraviolet irradiation exposure equipment is very expensive and it is not easy to produce the metal oxide film having a large area continuously.
Also, according to the formation method described in JP200-327310A, there is a problem that many producing steps are necessary, since the metal oxide sol must be beforehand changed into the metal oxide gel.
Further, according to the formation methods described in JPH9-157855A and JP200-327310A, there are no descriptions or suggestions regarding the formation of the predetermined surface irregularity as well as no referring to the specific means to form such surface irregularity stably.
Also, according to the formation method described in JP2008-177549A, it is necessary to provide the conductive layer including a metal film or a metal oxide film on the texturing layer having the surface irregularity and there is a problem that such a metal film or a metal oxide film are easy to exfoliate from the texturing layer.
Further, according to the formation method of the porous material described in JPH2-254192A, there are problems that many manufacturing steps are necessary and it is not easy to make the porous material precisely and stably.
On the other hand, conventionally, although electrically conductive layers comprising the metal oxide film (ITO or IZO) having a pattern are widely used as a transparent electrode, the predetermined patterns are usually formed by the etching treatment using the strong acid as an etchant solution, after formation of the metal oxide on the substrate by a vapor deposition process on the substrate.
However, there are problems that the etching speed for ITO or IZO etc is inherently slow, and if such etching speed is increased, the etching precision would be significantly decreased.
Further, the corrosion owing to the etchant solution (strong acid) residue easily occurs, and it is necessary to have the neutralization process of the etchant solution, a washing process having a considerable time and the conditioner process respectively in the manufacturing method.
Thus, the present inventors have keen studied the above mentioned problems, they have discovered that the metal oxide film having both a predetermined surface irregularity and a predetermined pattern or either, could be obtained by a thermal oxidation treatment or a plasma oxidation treatment easily and stably, after having formed both a predetermined surface irregularity and a predetermined pattern or either to the coated film which is coated a liquid material containing at least one of metal salts and metal complexes, and they have accomplished the present invention.
Namely, the objective of the present invention is to provide a method for easily and stably forming a metal oxide film having both a predetermined surface irregularity and a predetermined pattern or either, and having an excellent surface specific resistance and transparency and the like, without changing beforehand into the metal oxide gel from the metal oxide sol when the metal oxide film is formed.
Further, another objective of the present invention is to provide a metal oxide film having both a predetermined surface irregularity and a predetermined pattern or either obtained by the aforementioned method.